Computation of Relative Magnetic Helicity in Spherical Coordinates     

Kostas Moraitis  Étienne Pariat  Antonia Savcheva  Gherardo Valori 《Solar physics》2018,293(6):92

Magnetic helicity is a quantity of great importance in solar studies because it is conserved in ideal magnetohydrodynamics. While many methods for computing magnetic helicity in Cartesian finite volumes exist, in spherical coordinates, the natural coordinate system for solar applications, helicity is only treated approximately. We present here a method for properly computing the relative magnetic helicity in spherical geometry. The volumes considered are finite, of shell or wedge shape, and the three-dimensional magnetic field is considered to be fully known throughout the studied domain. Testing of the method with well-known, semi-analytic, force-free magnetic-field models reveals that it has excellent accuracy. Further application to a set of nonlinear force-free reconstructions of the magnetic field of solar active regions and comparison with an approximate method used in the past indicates that the proposed method can be significantly more accurate, thus making our method a promising tool in helicity studies that employ spherical geometry. Additionally, we determine and discuss the applicability range of the approximate method.  相似文献   

Feldspar composition as an efficient tool for tephra identification: a case study from Holocene and Lateglacial lacustrine sequences (Jura,France)          下载免费PDF全文

GWÉNOLÉ JOUANNIC  ANNE‐VÉRONIQUE WALTER‐SIMONNET  GILLES BOSSUET  CAROLE BEGEOT  ANNE‐LISE DEVELLE 《第四纪科学杂志》2015,30(6):569-583

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Observed Trends in Severe Weather Conditions Based on Humidex,Wind Chill,and Heavy Rainfall Events in Canada for 1953–2012     

Éva Mekis  Lucie A. Vincent  Mark W. Shephard  Xuebin Zhang 《大气与海洋》2015,53(4):383-397

Observed trends in severe weather conditions based on public alert statements issued by Environment Canada are examined for Canada. Changes in extreme heat and extreme cold events represented by various humidex and wind chill indices are analyzed for 1953–2012 at 126 climatological stations. Changes in heavy rainfall events based on rainfall amounts provided by tipping bucket rainfall gauges are analyzed for 1960–2012 at 285 stations. The results show that extreme heat events, defined as days with at least one hourly humidex value above 30, have increased significantly at more than 36% of the stations, most of which are located south of 55°N; days with nighttime hourly humidex values remaining above 20 have increased significantly at more than 52% of the stations, most of which are located south of 50°N. Extreme cold events represented by days with at least one hourly wind chill value below ?30 have decreased significantly at more than 76% of the stations across the country. No consistent changes were found in heavy rainfall events. Because city residents are very vulnerable to severe weather events, detailed results on changes in extreme heat, extreme cold, and heavy rainfall events are also provided for ten urban centres.  相似文献   

Reply to the Discussion by Roger Higgs on ‘Hummocky cross‐stratification‐like structures in deep‐sea turbidites: Upper Cretaceous Basque basins (Western Pyrenees,France)’ by Mulder et al., Sedimentology, 56, 997–1015     

THIERRY MULDER  PHILIPPE RAZIN  JEAN‐CLAUDE FAUGÈRES  JEAN GÉRARD 《Sedimentology》2011,58(2):571-577

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Earliest Triassic microbialites in Çürük Dag,southern Turkey: composition,sequences and controls on formation     

STEVE KERSHAW  SYLVIE CRASQUIN  MARIE‐BÉATRICE FOREL  CARINE RANDON  PIERRE‐YVES COLLIN  ERDAL KOSUN  SYLVAIN RICHOZ  AYMON BAUD 《Sedimentology》2011,58(3):739-755

The Permian–Triassic Boundary sequence at Çürük Dag, near Antalya, Turkey, begins with a major erosion surface interpreted as being the Late Permian lowstand, on which lies ca 0·4 m of grainstone/packstone composed of ooids, peloids and bioclasts. Most ooids are superficial coats on fragments of calcite crystals presumed to be eroded from crystal fans which are no longer present. The erosion surface is smooth and shows no evidence of dissolution; the grainstone/packstone contains intraclasts of the underlying wackestone, proving erosion. Next are 15 m of microbialite comprised of interbedded stromatolites, thrombolites, plus beds of planar limestones with small‐scale erosion. The latter comprise a complex interlayering of stromatolitic, thrombolitic and peloidal fabrics and precipitated crystal fans, which form a hybrid of microbialite and inorganic carbonate, together with bioclastic debris and micrite. The Çürük Dag microbialite sequence is repetitious; the lower part is more complex, with abundant stromatolites and hybrid microbialites. Some of the stromatolites are themselves hybrids composed of peloids and crystal fans. In the upper part of the sequence stromatolites are missing and the rock is composed mostly of recrystallized thrombolites that develop upwards from tabular to domal form. The domes form directly below small breaks in microbialite growth where very thin shelly micrites and grainstones/packstones are deposited. Repetition of facies may be controlled by sea‐level change; a deepening‐up model is consistent with the evidence. Stromatolites (with abundant crystal fans) dominate in shallower water, deepening through hybrid microbialite and interlayered sediments to thrombolite, probably no more than a few tens of metres deep, followed by breaks and renewal of microbialite growth. An interpretation of open marine fully oxygenated waters for microbialite growth is consistent with ongoing parallel work that has identified Bairdioid ostracods in the microbialite, a group known to be open marine. However, other researchers have proposed low oxygen conditions for Permian–Triassic boundary facies globally, so work continues to confirm whether the Çürük Dag microbialite grew in dysoxic or normally oxygenated conditions. The principal stimulus for post‐extinction microbialites is likely to be carbonate supersaturation of the oceans. The microbialite sequence is overlain by a further 25 m of grainstone/packstone (without microbialite), followed by Early Triassic shales. Overall, microbialites form a thin aggradational sequence during an overall relative sea‐level rise, consistent with global eustatic rise following the Late Permian lowstand.  相似文献   

Integration of sedimentology and ground‐penetrating radar for high‐resolution imaging of a carbonate platform     

STÉPHAN J. JORRY  GRÉGORY BIÉVRE 《Sedimentology》2011,58(6):1370-1390

Ground‐penetrating radar has not been applied widely to the recognition of ancient carbonate platform geometries. This article reports the results of an integrated study performed on an Upper Jurassic outcrop from the south‐east Paris basin, where coral bioherms laterally change into prograding depositional sequences. Ground‐penetrating radar profiles illustrate the different bedding planes and major erosional unconformities visible at outcrop. A ground‐penetrating radar profile conducted at the base of the cliff displays a palaeotopographic surface on which the outcropping bioherms settled. The excellent penetration depths of the ground‐penetrating radar (20 m with a monostatic 200 MHz antenna) images the carbonate platform geometries, ranging between outcrop workscale (a few metres) and seismic scale (several hundreds of metres). This study supports recent evidence of icehouse conditions and induced sea‐level fluctuations controlling the Upper Jurassic carbonate production.  相似文献   

Electron acceleration within coronal loops: A wave-particle process?     

D. Le QuÉau  A. Roux 《Solar physics》1987,111(1):19-22

A simple model as given which aims at explaining how electrons could be accelerated within solar coronal loops due to their trapping by quasi-monochromatic whistler waves.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.  相似文献   

Global Regularization of the Restricted Problem of Three Bodies     

Bálint Érdi 《Celestial Mechanics and Dynamical Astronomy》2004,90(1-2):35-42

The global regularizing transformations of the planar, circular restricted problem of three bodies are studied. It is shown that all these transformations can be written in the same general form which is the solution of a first order ordinary differential equation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Corporate responses to the CDM: the Indian pulp and paper industry     

KATI KULOVESI  MARÍA GUTIÉRREZ  PETER DORAN  MIQUEL MUŃOZ 《Climate Policy》2013,13(3):255-261

The key outcomes of the 2006 Nairobi Conference on Climate Change are described, with a particular emphasis on adaptation, the Clean Development Mechanism (CDM) and the future of the United Nations climate change regime beyond 2012. Based on an analysis of the key issues being negotiated, the Nairobi Conference can be understood as an important step in the larger process towards a future climate change regime. Its significance is in establishing the confidence and trust between the key players that will be necessary for the successful completion of the current phase of negotiations and agreement on the post-2012 climate change regime.  相似文献   

On some long time dynamical features of the Trojan asteroids of Jupiter     

Bálint Érdi  Emese Forgács-Dajka  Áron Süli 《Celestial Mechanics and Dynamical Astronomy》2013,117(1):3-16

The equation of motion of long periodic libration around the Lagrangian point $L_4$ L 4 in the restricted three-body problem is investigated. The range of validity of an approximate analytical solution in the tadpole region is determined by numerical integration. The predictions of the model of libration are tested on the Trojan asteroids of Jupiter. The long time evolution of the orbital eccentricity and the longitude of the perihelion of the Trojan asteroids, under the effect of the four giant planets, is also investigated and a slight dynamical asymmetry is shown between the two groups of Trojans at $L_4$ L 4 and $L_5$ L 5 .  相似文献